Vehicular Ad-hoc Networks (VANET) enable a number of applications, namely safety, transport efficiency or infotainment. These applications rely on the exchange of information between network nodes, i.e. vehicles, and can greatly benefit from information generated far away (e.g. to warn drivers of accidents and road works ahead). Important information can be propagated locally in vehicular networks via multiple hops between vehicles. Additionally, vehicular networks support data exchange using vehicle to infrastructure communications and remote information exchange, optionally with the support of a centralized entity, generally denominated Geoserver. However, the characteristics of vehicular networks, in particular the dynamically changing network topology or network partitioning, create additional challenges for successful data propagation/information dissemination.
Extensive research has been conducted in the broad area of information dissemination, which has the main objective of transferring data in a reliable manner between nodes participating in a communication network. The majority of the existing prior art methods focus on single-technology data dissemination, which can limit the solution optimality. In the context of vehicular network, the most common examples are short-range communications, e.g. ITS (Intelligent Transport Systems)-G5 (which is the European communication standard for vehicular communication), and cellular communications, e.g. Universal Mobile Telecommunications System (UMTS) or Long Term Evolution (LTE).
Both kinds of communications have different advantages and drawbacks. On the one hand, ITS-G5 has low latency but smaller coverage. On the other hand, cellular communications have higher coverage but also higher latency performance. For instance, in T. Mangel et al.: “A comparison of UMTS and LTE for vehicular safety communication at intersections”, in IEEE Vehicular Networking Conference, pp. 293-300, 13-15 Dec. 2010, the performance of cellular networks (UMTS, LTE) and ITS-G5 communication is compared as alternative means to exchange safety-critical information at intersections. Here, the authors conclude that cellular networks in isolation are not able to perform as well as ITS-G5 for this specific application type.
Along with the poor coverage/latency ratio, another problem prevalent in vehicular networks is limited message penetration due to insufficient infrastructure availability. Generally, one way to increase the dissemination area would be to deploy ITS-G5 Roadside Units (RSUs) for increasing the connectivity of vehicular ad hoc networks. However, several factors including cost, complexity, and existing systems (e.g. cellular networks), have impeded the deployment of RSUs.
On the other hand, with respect to cellular communication it should be noted that cellular networks show fragmentation due to multiple operators.
Regarding single-technology information dissemination, in many of the current solutions, message penetration is achieved through the infrastructure nodes which are usually placed at pre-defined locations (e.g. intersections, busy road segments). Due to dynamic nature of vehicular networks these static placement lacks the flexibility and may not provide the desired dissemination coverage. Few works in the literature propose using vehicles that act as temporary RSUs (e.g. can make brief stops during which they act as a communication bridge for other vehicles in the network).
For instance, Câmara et al.: “Multicast and Virtual Road Side Units for Multi Technology Alert Messages Dissemination” in IEEE International Conference on Mobile Adhoc and Sensor Systems (MASS), pp. 947-952, 17-22 Oct. 201 present the virtual RSU (vRSU) concept and shows its feasibility. However, the authors only alternatively use different communication technologies and do not consider the case of dissemination information to a geographical area, i.e. involving determining a set of vRSUs. Eckhoff et al.: “Cooperative Awareness At Low Vehicle Densities: How Parked Cars Can Help See Through Buildings” in IEEE Global Telecommunications Conference, pp. 1-6, December 2011 propose the use of parked cars as relay nodes in vehicular networks in especially challenging propagation conditions (e.g. urban intersections). Tonguz et al.: “Cars as Roadside Units: A Self-Organizing Network Solution” in IEEE Communications Magazine, vol. 51, no. 12, pp. 112-120, December 2013 propose a distributed algorithm for selecting vehicles as temporary RSU, which stop for a short time interval for rebroadcasting messages. In general, mobile infrastructure seems to be a very promising solution for improving vehicular communications; however, there is no proper approach which handles multiple requirements which are relevant in vehicular networks.